The advent of higher speed and more complex copiers and reproduction machines that generate an image on a line-by-line basis brought with it a corresponding increase in the complexity of machine control wiring and logic. While this complexity manifests itself in many ways, perhaps the most onerous involves the inflexibility of the typical control logic/wiring systems. For it to be appreciated, simple unsophisticated machines with relatively simple control logic and wiring can be altered and modified easily to incorporate changes, retrofits and the like. Servicing and repair of the control logic is also fairly simple. On the other hand, some modern high speed machines which often include a sorter, a document handler, choice of copy sites, multiple paper trays, jam protection and the like, have extremely complex logic systems making even the most minor changes and improvements in the control logic difficult, expensive and time consuming. In servicing or repairing the machine control logic paper handling systems, electromechanical components, etc., may similarly entail substantial difficulty, time and expense.
Nonetheless, the maintenance of complex reproduction machines has become an increasingly important aspect in the commercial reproduction and sale of such machines. As these machines grow larger, more complex, faster and more expensive, it has become increasingly important to take measures ensuring the machines continue reliable operation. As these machines are indispensable to their users, an increasingly important feature of such machines is their reliability. When a machine does malfunction, it is desirable that it be fixed in as short a time as possible.
As a result of these needs, much work has been done to improve the on-board diagnostic capability of these machines. With such a machine capability, a service representative, or a trained user can easily and quickly determine the causes of the malfunction. In the case of a service representative, based on such diagnostic report from the machine, action may be taken to effectuate an appropriate repair.
In a complex piece of hardware such as a copier or reproduction machine, it is difficult to tell if various machine functions are happening in the proper sequence. Usually sensors, switches, valves and motors are monitored by an internal computer and fault conditions are recorded for later playback by a service person. This record enables the service person to quickly identify the source of the problem and repair it. This type of apparatus is disclosed in U.S. Pat. Nos. 4,062,061 and 4,739,366. The drawback of such an apparatus is that it requires additional equipment to display and analyze the stored data, usually at a later time. Also, such data are difficult to directly relate to the actual image on the paper, should an image artifact occur.
In a laser copier or laser printer, it is extremely important to maintain a smooth rotation of the exposing drum during the time that the image is being recorded. Any machine vibration or change in velocity will cause an artifact in the final output copy that will appear as a dark or light band. It is usually very difficult to determine the source of these velocity perturbations. Usually, a record is made of all the time durations of machine component activations and this record is analyzed to determine if any activations occurred at the same time as the artifact. It is not a simple task to correlate the simple relationships back to the final paper image.